For rendering Google Maps in virtual reality on iOS using Google Cardboard, you can explore the following VR SDKs and tools:

SDK for Google VR (Cardboard): Google's official VR developer SDK, which works with iOS. supports encounters with Google Cardboard. Although 360-degree environments can be rendered, direct Google Maps integration necessitates special development utilizing the Google Maps SDK for iOS.

Cardboard SceneKit: It is possible to render 3D content using Apple's SceneKit and integrate it with Google Cardboard for virtual reality. Map tiles can be retrieved via the Google Maps SDK for iOS and then rendered as textures in SceneKit.

Google Cardboard and Unity: Using Google Maps Platform APIs, Unity can load Google Maps as textures and facilitate VR development. To integrate VR, use the Cardboard XR Plugin for iOS.

Libraries that are open source: Although not actively updated, ViroReact can still be used for simple virtual reality projects. Using WebXR with Three.js: a web-based VR method that is restricted on iOS because to Safari's incomplete WebXR compatibility.

Note: Because to license and API restrictions, Google Maps cannot be displayed directly in virtual reality. Using the Google Maps Platform API, you will need to retrieve map tiles or 3D data and manually render it into your virtual reality environment.